Solar reflective composite granules and method of making solar reflective composite granules

ABSTRACT

A method of making a plurality of composite granules can include: forming green body granules comprising an aluminosilicate; heating the green body granules to form sintered granules; cooling the sintered granules according to a cooling regime, wherein the cooling regime comprises a temperature hold between 700° C. and 900° C. for at least one hour. In a particular embodiment, the aluminosilicate for making the composite granules can have a particle size less than 150 μm. The composite granules are particularly suitable as roofing granules and can have a desired combination of high solar reflectance SR and low lightness L*, a low bulk density, good weather resistance and strength.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority under 35 U.S.C. § 119(e) to U.S.Provisional Patent Application No. 62/441,178 entitled “SOLAR REFLECTIVECOMPOSITE GRANULES AND METHOD OF MAKING SOLAR REFLECTIVE COMPOSITEGRANULES,” by Tracy H. PANZARELLA et al., filed Dec. 31, 2016, which isassigned to the current assignee hereof and incorporated herein byreference in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates to solar reflective composite granulesincluding an aluminosilicate. The disclosure further relates to a methodof making the solar reflective composite granules.

BACKGROUND

Solar reflectivity has gained large prominence as a roofing feature dueto regulatory pressure and customer preference. Traditionally, toproduce solar reflective (SR) granules, standard base rock is crushed toa particle size of about 0.5 mm to 1.5 mm and the sized particles arecoated to cover the granules with a solar reflective layer. The SRcoating of the granules contributes to a significant amount of thematerial, energy, time, and total costs of producing the SR granules.Moreover, when crushing the base rock, about 40 wt % to 50 wt % of thecrushed stone is considered as waste material, also called granulefines, since the particle sizes are lower than the desired size rangefor roofing granules.

There is a need for more economic ways of manufacturing roofing granuleswith a high solar reflectance. Furthermore, there is a continuing needfor roofing granules with a high solar reflectance but low lightness L*value.

SUMMARY

According to one embodiment, a method of making a plurality of compositegranules, comprising: forming green body granules comprising analuminosilicate; heating the green body granules to form sinteredgranules; cooling the sintered granules according to a cooling regime,wherein the cooling regime comprises a temperature hold between 700° C.and 900° C. for at least one hour.

According to another embodiment, a method of making a plurality ofcomposite granules, comprising: forming a plurality of green bodygranules comprising an aluminosilicate; heating the green body granulesto form sintered granules; and cooling the sintered composite granulesat a cooling rate of not greater than 2° C. per minute to a temperatureof 750° C.

According to a further embodiment, a plurality of composite granules,comprising: a bulk density of not greater then 1 g/cm³; an amount ofaluminosilicate of at least 50 wt %; an amount of aluminum trihydrate(ATH) of at least 2 wt %; a solar reflectance of at least 30%; an L*value of not greater than 50; and an average crush strength of at least45 N.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may be better understood, and its numerousfeatures and advantages made apparent to those skilled in the art byreferencing the accompanying drawings.

FIG. 1A includes an illustration of commercial stone crushing to obtainrock-based roofing granules.

FIG. 1B includes an illustration of the process of the presentdisclosure according to one embodiment.

FIG. 2 includes a graph showing the effect of the ATH median particlessize and concentration with regard to an increase in solar reflectanceof granule fines according to certain embodiments.

FIG. 3 includes a graph showing the force to crush one single compositegranule according to certain embodiments, as well as the force requiredfor crushing commercial roofing granules of different structure.

FIG. 4 includes a graph showing freeze/thaw durability of the compositegranules according to certain embodiments in comparison to commercialroofing granules of different structure.

FIG. 5 includes an illustration of a testing device for measuring theabrasion resistance of roofing granules according to the test method ofthe Asphalt Roofing Manufacturer's Association (ARMA 1993).

FIG. 6 includes a graph showing the abrasion resistance measuredaccording the ARMA method demonstrated in FIG. 5 of composite granulesaccording to certain embodiments, in comparison to commercial roofinggranules of different structure.

FIG. 7 includes a graph showing bulk densities of composite granulesaccording to certain embodiments in comparison to commercial roofinggranules of different structure.

DETAILED DESCRIPTION

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,method, article, or apparatus that comprises a list of features is notnecessarily limited only to those features but may include otherfeatures not expressly listed or inherent to such process, method,article, or apparatus.

As used herein, and unless expressly stated to the contrary, “or” refersto an inclusive-or and not to an exclusive-or. For example, a conditionA or B is satisfied by any one of the following: A is true (or present)and B is false (or not present), A is false (or not present) and B istrue (or present), and both A and B are true (or present).

Also, the use of “a” or “an” are employed to describe elements andcomponents described herein. This is done merely for convenience and togive a general sense of the scope of the invention. This descriptionshould be read to include one or at least one and the singular alsoincludes the plural unless it is obvious that it is meant otherwise.

Various embodiments of the present disclosure will now be described, byway of example only, with reference to the accompanying drawings.

The present disclosure relates to roofing granules made by an economicprocess, wherein the roofing granules may have a light weight anddesired strength, weather resistance, and optical properties, such assolar reflectance (SR) and lightness L*.

As used herein, the term “granule fines” is intended to mean small rockparticles obtained by crushing of rock, wherein the granule fines havinga particle size smaller than 0.5 mm. In particular embodiments, thegranule fines have a particle size below 150 μm.

As used herein, the term “green body granules” is intended to meangranules that include granule fines, a binder, and a solvent and havenot being subjected to high temperature sintering.

As used herein, the term “composite granules” is intended to meangranules obtained after high temperature sintering of the green bodygranules. In a particular embodiment, the sintering temperature may beat least 1000° C.

As used herein, by “mesh size” is meant ASTM U.S. standard mesh sizeunless otherwise indicated.

FIG. 1A gives an overview of a commercial process of makingaluminosilicate rock-based roofing granules, starting from crushing baserock to obtain granules having a particle size typically in a rangebetween 0.5 and 1.5 mm, and a fraction containing fines with a particlessize of smaller then 0.5 mm, which are granule fines. Before theinventors' discovery, the granule fines may have been considered waste;however, the inventors have developed a process to recover a significantportion of the granule fines that can be useful as roofing granules orfor other applications.

In embodiments, the method of the present disclosure relates to themaking of composite granules from the aluminosilicate granule finesobtained as by-product from the rock crushing as shown in FIG. 1A. Inembodiments, as further demonstrated in FIG. 1B, the composite granulesof the present disclosure can be made by a method using thealuminosilicate granule fines of FIG. 1A as starting material. Themethod may include sieving the granule fines into fractions ofparticular particle size ranges (1.1); granulating the fractionedgranule fines together with a binder and a solvent to form green bodygranules (1.2); sizing the green body granules (1.3); high temperaturesintering the sized green body granules (1.4); and cooling the sinteredgranules according to a controlled cooling regime (1.5). The compositegranules of the present disclosure are characterized by having a lightweight, good strength and wearability and desirable optical properties,making them very suitable for the use as low-cost roofing granules.

In a particular embodiment, the granule fines used as starting materialin the process of the present disclosure can be an aluminosilicatematerial from crushed base rock, such as rhyolite, andesite, basalt, ormeta-basalt.

In embodiments, the aluminosilicate granule fines may be sieved toobtain granule fines having a particle size not greater than 250 μm,such as not greater than 200 μm, not greater than 180 μm, not greaterthan 150 μm, or not greater than 120 μm. In other embodiments, theparticle size of the aluminosilicate can be at least 0.5 μm, such as atleast 1 μm, at least 5 μm, at least 10 μm, at least 20 μm, at least 30μm, or at least 40 μm. The particles size of the aluminosilicate granulefines can be a value between any of the minimum and maximum values notedabove, such as from 0.5 μm to 200 μm, from 10 μm to 150 μm, or from 30μm to 120 μm.

In further embodiments, the amount of the aluminosilicate granule finesbased on the total weight of the green body granules formed duringgranulation may be at least 50 wt %, such as at least 60 wt %, at least70 wt %, at least 80 wt %, or at least 90 wt % based on the total weightof the green body granules. In yet other embodiments, the amount ofaluminosilicate may be not greater than 99 wt %, such as not greaterthan 98 wt %, or not greater than 95 wt % based on the total dry weightof the green body granules. The amount of aluminosilicate can be a valuewithin any of the minimum and maximum values noted above, such as from50 wt % to 99 wt %, from 60 wt % to 98 wt %, or from 70 wt % to 95 wt %,based on the total dry weight of the green body granules.

The binder used for making the green body granules of the presentdisclosure may not be particularly limited, as long it can properlyfunction as a binder. In a particular embodiment, the binder can bemodified starch, for example, ethoxylated starch. In aspects, the amountof the binder can be at least 0.1 wt %, such as at least 0.3 wt %, or atleast 0.5 wt % based on a total weight of the green body granules. Inother aspects, the amount of binder may be not greater than 5 wt %, suchas not greater than 3 wt %, not greater than 1 wt %, or not greater than0.8 wt % based on a total weight of the green body granules.

The type of solvent for forming the green body granules may also not belimited. In a particular embodiment, the solvent can be water. Incertain aspects, the solvent can have an amount of at least 0.5 wt %, atleast 1 wt %, at least 2 wt %, at least 3 wt %, or at least 5 wt % basedon the total weight of the green body granules. In other aspects, thesolvent may not be greater than 20 wt %, such as not greater than 15 wt%, not greater than 12 wt %, or not greater than 10 wt % based on thetotal weight of the green body granules.

In certain embodiments, the green body granules can be formed bygranulating a mixture comprising at least 50 wt % aluminosilicategranule fines, at least 0.5 wt % binder, and at least 10 wt % solventbased on the total weight of the green body granules.

In particular embodiments, the granulating mixture can containaluminosilicate granule fines in an amount of at least about 80 wt %, abinder of at least 0.5 wt %, and water of at least about 10 wt % basedon the total weight of the granulating mixture.

In embodiments, the sizing (1.3) of the green body granules formed fromthe granulating mixture before high temperature sintering may beconducted by removing very large and very fine particle via sieving. Inparticular embodiments, the green body granules after sizing (1.3) andbefore high temperature sintering (1.4) may be not greater than 5 mm,such as not greater than 4 mm, not greater than 3.5 mm, not greater then3.0 mm, not greater then 2.5 mm, not greater than 2.0 mm, or not greaterthan 1.5 mm. In other embodiments, the size of the green body granulesmay be at least 0.3 mm, such as at least 0.4 mm, or at least 0.5 mm. Thegreen body granules after sizing (1.3) can have a value between any ofthe minimum and maximum values noted above, such as from 0.3 mm to 5 mm,from 0.5 mm to 3.0 mm, or from 0.7 mm to 2.0 mm.

The high temperature sintering (1.4) of the green body granules can beconducted such that the green body granules are heated up to a maximumsintering temperature, keeping the temperature at the maximum sinteringtemperature for a certain time period, and thereafter conducting acontrolled cooling (1.5) of the sintered granules.

In certain embodiments, the maximum temperature of the high temperaturesintering (1.4) may be not greater than 1300° C., such as not greaterthan 1250° C., not greater than 1200° C., not greater than 1150° C., notgreater than 1100° C., or not greater than 1075° C. In other particularembodiments, the sintering temperature may be at least 1000° C., such asat least 1020° C., or at least 1050° C. The maximum sinteringtemperature may be a value between any of the maximum and minimum valuesnoted above, such as from 1000° C. to 1300° C., from 1025° C. to 1150°C., or from 1050° C. to 1100° C.

In embodiments, the time for heating at the maximum sinteringtemperature can be at least 1 minute, at least 5 minutes, at least 10minutes, or at least 30 minutes. In other embodiment, the heating at themaximum sintering temperature may be not longer than 5 hours, such asnot longer than 3 hours, not longer than 2 hours, or not longer than 1hour. The time for heating at the maximum sintering temperature can havea value between and or the minimum and maximum values note above, suchas from 1 minute to 3 hours, from 5 minutes to 1 hour, or from 10minutes to 45 minutes.

Unexpectedly, the cooling treatment regime can affect the solarreflectance of the obtained composite granules. If during controlledcooling of the granules (1.5) a temperature hold is conducted at atemperature range between 700° C. and 900° C., the obtained compositegranules can have a higher solar reflectance than composited granulesmade without a temperature hold during cooling, wherein the temperatureis allowed to fall freely at the natural rate of the furnace withoutcontrolling the speed during the temperature decrease, also calledherein “free cooling.”

A similar effect on the solar reflectance of the composite granules canbe observed if the cooling is conducted very slowly at a cooling ratenot greater than 2° C. per minute, preferably not greater than 1° C. perminute, or not greater than 0.5° C. per minute.

In certain embodiments, the temperature at the temperature hold may benot greater than 900° C., such as not greater than 875° C., not greaterthan 850° C., or not greater than 825° C. In other certain embodiments,the temperature hold me be at a temperature of at least 700° C., such asat least 725° C., at least 750° C., at least 775° C., or at least 800°C. The temperature hold can be at a value between any of the minimum andmaximum values note above, such as from 700° C. to 900° C., from 725° C.to 875° C., or from 750° C. to 850° C.

In embodiments, the time for holding the temperature during cooling ofthe granules can be at least 0.5 hours, such as at least 1.0 hour, atleast 1.5 hours, or at least 2 hours. In other embodiments, the time forholding the temperature may be not greater than 6 hours, such as notgreater than 5 hours, or not greater than 4 hours. The temperatureholding time during cooling can be a value between any of the minimumand maximum values noted above, such as from 1.0 hour to 6 hours, from1.5 hours to 5 hours, or from 2 hours to 4 hours.

In certain embodiments, the difference in solar reflectance ΔSR ofcomposite granules subjected to a temperature hold (SR_(TH)) incomparison to composite granules made without including a temperaturehold (SR_(F)) can be at least 3%, such as at least 4%, at least 5%, orat least 6%, wherein ΔSR=SR_(TH)−SR_(F).

Unexpectedly, a temperature hold during cooling in the range of 700-900°C. can increase the solar reflectance of the roofing granules, yet, thelight intensity L* may be not significantly affected by the temperaturehold, and the L* values remain substantially constant. This allows themaking of composite granules with a high solar reflectance but acorresponding low lightness L*.

In a particular embodiment, the roofing granules of the presentdisclosure can have a solar reflectance of at least 25% and an L* valuenot greater than 50 without any applied coatings on the surface of thecomposite granules.

Furthermore, unexpectedly, the maximum sintering temperature can alsoaffect the solar reflectance of the composite granules. In oneparticular embodiment, an increase of 25° C. in the maximum sinteringtemperature, from 1075° C. to 1100° C., can lead to a significant dropin solar reflectance of about 20 points. Not to be bound by theory, thestrong decrease in solar reflectance and development of a relativelydark color after reaching a certain sintering temperature may depend onthe type of aluminosilicate rock from which the granule fines areobtained, particularly of the iron content within such rock. At acertain temperature, when sintering causes phase changes within thesintered material and partial fusing and melting, it appears that Feions can migrate to the surface of the granules, together with theforming of a glassy phase on the granule surface, and decrease porosity.

Accordingly, in order to obtain roofing composite granules with desiredoptical properties and strength, depending on the type ofaluminosilicate, a maximum sintering temperature may be selected closeto the point at which a large drop in solar reflectance and lightness ofthe composite granules occurs, which is also named herein as “color droptemperature (T_(cd)).” As used herein, the T_(cd) is intended to mean asintering temperature at which a decrease in solar reflectance(ΔSR_(cd)) of at least 8% SR occurs, such as at least 9% SR, at least10% SR, at least 15% SR, or at least 20% SR. In one particularembodiment, the color drop temperature T_(cd) can be within a range from1075° C. to 1100° C. with a color drop of at least 10% SR.

Selecting a maximum sintering temperature too far below the color droptemperature T_(cd) can have the disadvantage of forming compositegranules with insufficient strength. In certain embodiments, the maximumsintering temperature may be not less than 50° C. lower than the colordrop temperature, such as not less than 25° C., or not less than 20° C.In other certain embodiments, the maximum sintering temperature can benot greater than 50° C. than the color drop temperature, such as notgreater than 25° C., not greater than 10° C., or at the same temperatureas the color drop temperature.

In other particular embodiments, the solar reflectance and lightness L*of the composite granules of the present disclosure may be furtherincreased by adding white dopants during granulation (1.2) when formingthe green body granules. Non-limiting examples of white dopants caninclude aluminum trihydrate (ATH), titanium dioxide, zinc oxide, ormagnesium hydroxide.

Unexpectedly, the highest increase in solar reflectivity could beobtained when ATH was added during the granulation step, in comparisonto other dopants, such as titanium dioxide, zinc oxide, or magnesiumhydroxide. Accordingly, in a particular embodiment, the compositegranules of the present disclosure are essentially free of TiO₂, ZnO₂,and Mg(OH)₂. Essentially free means unavoidable impurities or amounts ofless than 0.1 wt % based on the total weight of the composite granules.

The amount of ATH added to the granulating mixture to form the greenbody granules can be at least 1 wt %, such as at least 2 wt %, at least3 wt %, at least 4 wt %, or at least 5 wt % based on the total weight ofthe green body granules. In other particular embodiments, the amount ofATH may be not greater than 12 wt %, such as not greater than 10 wt %,or not greater than 8 wt %. The amount of ATH added to the granulemixture can be a value between any of the minimum and maximum valuesnoted above, such as from 1 wt % to 12 wt %, from 2 wt % to 8 wt %, orfrom 3 wt % to 5 wt % based on the total weight of the green bodygranules.

In further particular embodiments, the median particle size of the ATHadded to the granulation mixture can be at least 0.1 μm, such as atleast 0.5 μm, or at least 1 μm. In other particular embodiments, themedian particle size of ATH may be not greater than 40 μm, such as notgreater than 35 μm, not greater than 30 μm, not greater than 25 μm, notgreater than 20 μm, not greater than 15 μm, not greater than 10 μm, ornot greater than 5 μm. The median particles size of the ATH can be avalue between any of the minimum and maximum values note above, such asfrom 0.1 μm to 40 μm, from 1 μm to 20 μm, from 1 μm to 10 μm, or from0.5 μm to 5 μm. A particularly beneficial increase in solar reflectancecan be obtained with ATH having a particle size range within 1 μm and 10μm.

In particular embodiments, adding ATH as dopant to the granulatingmixture may result in an increase in solar reflectance of the compositegranules by at least 50% based on the solar reflectance of the compositegranules without dopants, such as at least 60%, at least 70%, at least80%, at least 90%, or at least 100%. For example, the solar reflectanceSR of composite granules can be increased from an SR of 19% to an SR of39% (which is an increase of 105%) by adding 5 wt % ATH to the granulefines, as shown in Example 2.

The composite granules of the present disclosure obtained by the abovedescribed process can have a high solar reflectance SR together with acomparable low lightness L*, a low weight (low bulk density), goodstrength and weather resistance, which makes them particularly suitableas roofing granules.

In embodiments, the composite granules of the present disclosure canhave a solar reflectance of at least 25%, such as at least 30%, andleast 35%, at least 37%, at least 40%, at least 43%, at least 45%, atleast 47%, or at least 50%.

In other embodiments, the composite granules can have a lightness L* ofnot greater than 60, such as not greater than 55, not greater than 50,not greater than 45, or not greater than 40. In yet other embodiments,the lightness L* may be at least 15, such as at least 20, or at least25.

The strength of the composite granules of the present disclosure,expressed in the crush strength measured by the test method as specifiedherein, can be at least 40 N, such as at least 42 N, at least 45 N, atleast 47 N, or at least 50 N.

The composite granules of the present disclosure can further possess ahigh freeze/thaw durability. The freeze/thaw durability was tested tosimulate the environment on the roof and to measure its effect on thecomposite granules. During the test, the granules are subjected tomultiple freeze/thaw cycles, each cycle including submerging thegranules in water, freezing the granules, and then defrosting at roomtemperature. The testing results after 10 to 30 cycles showed that evenafter 30 freeze thaw cycles, at least 98 wt % of the composite granulesremained on a 40 mesh size screen. In particular embodiments, after anexposure to 30 freeze/thaw cycles, the composite granules of the presentdisclosure can remain at least 98.5 wt % or at least 99 wt % of itsoriginal total weight.

The composite granules of the present disclosure can further have anabrasion resistance which is similar to the abrasion resistance ofcommercial rock-based roofing granules. Under abrasion resistance, asused herein, should be understood a percent breakdown of the granules ifsubjected to the granule breakdown test of the Asphalt RoofingManufacturer's Association (ARMA 1993), which simulates the granuleprocessing and handling conditions throughout a typical shingle makingprocess, and is in detail described in the experimental part of thepresent disclosure.

In embodiments, the breakdown of the composite granules if subjected tothe ARMA test is not greater than 6 wt %, such as not greater than 7 wt%, not greater than 8 wt %, or not greater than 9 wt %.

A further particular advantage of the composite granules of the presentdisclosure is its low bulk density. In embodiments, the bulk density isnot greater than 1.2 g/cm³, such as not greater than 1.1 g/cm³, notgreater than 1.0 g/cm³, or not greater than 0.98 g/cm³. In otherembodiments, the bulk density is at least 0.6 g/cm³, such as at least0.7 g/cm³, or at least 0.8 g/cm³, or at least 0.9 g/cm³. The bulkdensity can be a value between any of the minimum and maximum valuesnoted above, such as from 0.7 g/cm³ to 1.2 g/cm³, from 0.8 g/cm³ to 1.1g/cm³, or from 0.9 g/cm³ to 1.0 g/cm³.

The above described properties of the composite granules of the presentdisclosure may all relate the to composite granules being free of acoating

In particular embodiments, the roofing granules may optionally includeone or more coating layers. Possible type of coatings can be a pigmentcoating.

Unexpectedly, a pigment coating can lower the lightness L* of thecomposite granules but can maintain the solar reflectance. In aparticular embodiment, the pigment coating can lower the L* value of theuncoated composite granules by at least 1% and does not lower the solarreflectivity of the uncoated composite granules.

A pigment coating may further improve the abrasion resistance,freeze/thaw durability and crush strength of the composite granules, asfurther shown in the examples.

Many different aspects and embodiments are possible. Some of thoseaspects and embodiments are described herein. After reading thisspecification, skilled artisans will appreciate that those aspects andembodiments are only illustrative and do not limit the scope of thepresent invention. Embodiments may be in accordance with any one or moreof the embodiments as listed below.

EMBODIMENTS Embodiment 1

A method of making a plurality of composite granules, comprising:forming green body granules comprising an aluminosilicate;

heating the green body granules to form sintered granules;cooling the sintered granules according to a cooling regime, wherein thecooling regime comprises a temperature hold between 700° C. and 900° C.for at least one hour.

Embodiment 2

A method of making a plurality of composite granules, comprising:forming a plurality of green body granules comprising analuminosilicate;

heating the green body granules to form sintered granules; andcooling the sintered composite granules at a cooling rate of not greaterthan 2° C. per minute to a temperature of 750° C.

Embodiment 3

The method of embodiment 1, wherein the temperature hold is conducted ata temperature range between 800° C. and 900° C., such as between 850° C.and 900° C.

Embodiment 4

The method of embodiments 1 or 3, wherein the temperature hold is atleast 2 hours, such as at least 3 hours, or at least 5 hours.

Embodiment 5

The method of embodiments 1, 3, or 4, wherein the temperature hold isnot longer than 15 hours, such as not longer than 12 hours, or notlonger than 10 hours.

Embodiment 6

The method of embodiment 2, wherein the cooling rate is not greater than1° C./minute or not greater than 0.5° C./minute to a temperature of750°.

Embodiment 7

The method of any of embodiments 1 or 3-5, wherein a difference in solarreflectance ΔSR of a SR of composite granules subjected to thetemperature hold (SR_(TH)) in comparison to a SR of composite granulesnot subjected the temperature hold (SR_(F)) is at least 3%, such as atleast 4%, at least 5%, or at least 6%, with ΔSR=SR_(TH)−SR_(F).

Embodiment 8

The method of any of the preceding embodiments, wherein the solarreflectance of the composite granules is at least 25%, such as at least28%, or at least 30%.

Embodiment 9

The method of any of the preceding embodiments, wherein the L* value ofthe composite granules is not greater than 50, such as not greater than48, or not greater than 45.

Embodiment 10

The method of any of the preceding embodiments, wherein forming of thegreen body granules includes adding of a solvent and at least 0.5 wt %of a binder based on the total weight of the green body granules.

Embodiment 11

The method of embodiment 10, wherein the binder is modified starch.

Embodiment 12

The method of embodiment 10, wherein the solvent is water.

Embodiment 13

The method of any of the preceding embodiments, wherein forming of thegreen body granules includes adding of ATH in an amount of at least 2 wt%, such as at least 3 wt %, at least 5 wt %, or at least 7 wt % based onthe total dry weight of the green body granules.

Embodiment 14

The method of embodiment 13, wherein an amount of ATH in the green bodygranules is not greater than 20 wt %, such as not greater than 15 wt %,or not greater than 10 wt % based on the total dry weight of the greenbody granules.

Embodiment 15

The method of embodiments 13 or 14, wherein the ATH has a medianparticles size not greater than 30 μm, such as not greater than 25 μm,not greater than 20 μm, not greater than 10 μm, or not greater than 5μm.

Embodiment 16

The method of any of the preceding embodiments, further including sizingthe green body granules to a size of at least 0.3 mm and not greaterthan 3.0 mm.

Embodiment 17

The method of any of the preceding embodiments, wherein heating isperformed up to a maximum sintering temperature of at least 1000° C.,such as at least 1025° C., or at least 1050° C.

Embodiment 18

The method of any of the preceding embodiments, wherein heating isperformed up to a maximum sintering temperature not greater than 1300°C., such as not greater than 1250° C., not greater than 1200° C., notgreater than 1150° C., or not greater than 1100° C.

Embodiment 19

The method of embodiments 17 or 18, wherein the maximum sinteringtemperature is within a range of ±50° C. of a color drop temperatureT_(cd) of the aluminosilicate, the T_(cd) being a sintering temperaturewherein a decrease in solar reflectance (ΔSR_(cd)) of at least 8% SRoccurs.

Embodiment 20

The method of embodiment 19, wherein the maximum sintering temperatureis not less than 25° C. and not greater then 10° C. of the color droptemperature T_(cd) of the aluminosilicate.

Embodiment 21

The method of embodiments 19 or 20, wherein the color drop temperatureT_(cd) ranges from 1075° C. to 1100° C.

Embodiment 22

The method of any of the preceding embodiments, wherein thealuminosilicate is obtained from a natural rock.

Embodiment 23

The method of embodiment 22, wherein the natural rock includes rhyolite,andesite, basalt, meta-basalt, or any combination thereof.

Embodiment 24

The method of any of the preceding embodiments, wherein the amount ofaluminosilicate in the green body granules is at least 50 wt %, such asat least 60 wt %, at least 70 wt %, at least 80 wt %, at least 90 wt %,or at least 95 wt % based on the total dry weight of the green bodygranules.

Embodiment 25

The method of any of the preceding embodiments, wherein thealuminosilicate in the green body granules has an average particle sizenot greater than 250 μm, such as not greater than 200 μm, not greaterthan 180 μm, not greater than 150 μm, not greater than 120 μm, or notgreater than 100 μm.

Embodiment 26

The method of any of the preceding embodiments, wherein thealuminosilicate in the green body granules has an average particle sizeof at least 30 μm, such as at least 35 μm, at least 40 μm, or at least45 μm.

Embodiment 27

The method of any of the preceding embodiments, wherein a bulk densityof the composite granules is not greater than 1.0 g/m³.

Embodiment 28

The method of any of the preceding embodiments, wherein the compositegranules have an average crush strength of at least 45 N.

Embodiment 29

The method of any of the preceding embodiments, wherein the compositegranules have a roundness of at least 0.9.

Embodiment 30

The method of any of the preceding embodiments, wherein the green bodygranules are essentially free of TiO₂, ZnO₂, and Mg(OH)₂.

Embodiment 31

The method of any of the preceding embodiments, further comprisingapplying a pigment coating on the composite granules.

Embodiment 32

The method of embodiment 31, wherein the pigment coating lowers the L*value of the composite granules by at least 1% and does not lower thesolar reflectivity of the composite granules.

Embodiment 33

A plurality of composite granules, comprising:

a bulk density not greater then 1.0 g/cm³;an amount of aluminosilicate of at least 50 wt % based on the totalweight of the plurality of composite granules;an amount of aluminum trihydrate of at least 2 wt % based on the totalweight of the plurality of composite granules;a solar reflectance of at least 25%;an L* value of not greater than 50; and aan average crush strength of at least 45 N.

EXAMPLES

The following non-limiting examples illustrate the concepts describedherein.

Example 1

Evaluating granule fines regarding the effect of sintering and coolingconditions on SR and L*:

Granule fines of natural rock rhyolite (<0.5 μm) were sieved into twodifferent size fractions: a) coarse powder with a particles size of150-250 μm and b) fine powder with a particle size smaller than 150 μm.

From both powder fractions, cylinder coupons were pressed under apressure of 1000 psi, using per coupon 10 g granule fines. One couponhad a diameter size of 2 inches and a height of 0.5 inch.

The coupons were sintered in a furnace by heating at rate of 5°C./minute up to the maximum set sintering temperature in a range of1000° C. to 1150° C., depending on the type of experiment. When themaximum sintering temperature was reached, the temperature wasmaintained for one hour at the maximum temperature, and thereafter thecoupons were allowed to “free cooling” at the natural rate of thefurnace.

The coupons were analyzed by the optical parameters SR and L* on the topsurface of the coupons. As can be seen in Table 1, the coupons made ofthe fine powder fraction had much higher SR and L* values then thecoupons of the course powder fraction up to a sintering temperature ofabout 1050° C. A sintering temperature higher than 1050° C. resulted ina large darkening of the color of the coupons, and a difference of SRand L* between the coupons of the fine and the coarse fraction becamemuch lower.

TABLE 1 Sintering coupons of coarse and fine fraction of granule finesat varying temperatures Sintering Sintering Sintering 1000° C. max 1050°C. max 1100° C. max Fines size [μm] SR L* SR L* SR L* <100 μm (fine) 4457 39 51 19 40 150-250 μm 29 48 27 47 17 39.5 (coarse)

In view of the higher SR and L* values of the fine fraction (<150 μm) upto a temperature of 1050° C., further experiments were conducted onlywith coupons of the fine fraction. Specifically, the temperature rangeof 1075° C. and 1100° C. was investigated, at which a large drop in ofthe SR and the L* values could be observed, but also an increase instrength.

Table 2 summarizes the results with further focus on different coolingprofiles. A temperature holding period at 850° C. between 2 and 5 hoursresulted in samples having a 4 to 5 point higher solar reflectance (SR)then samples that were allowed to cool freely, without a temperatureholding period. Surprisingly, the different cooling profiles had noeffect on the color of the coupons. The measured L* values wereidentical for coupons with and without holding period during cooling.

It can be further seen from Table 2, that just a minor increase of themaximum sintering temperature from 1075° C. to 1100° C. resulted in asignificant decrease of the SR values and darkening of the granules. Notwishing to be bound by theory, the decrease in solar reflectance anddevelopment of a dark color after reaching a certain maximum sinteringtemperature appears to be a complex process, including an increase of Feions on the surface of the granules, the forming of a glassy phase onthe surface, and a decrease in porosity.

TABLE 2 Coupons of fine fraction of granule fines (<150 μm) subjected todifferent sintering and cooling profile Sintering Sintering 1075° C. max1100° C. max SR L* SR L* Free cool 32 47.5 17 39.8 2 hours hold at 850°C. 36 19 5 hours hold at 850° C. 37 48 20 40 Cooling rate 2° C./min to35 19 750° C.

Example 2

Adding different types of dopants to granule fines.

Coupons were made of granule fines <150 μm according to the sameprocedure as described in Example 1, except that in addition to thegranule fines, different types of white dopants were added in an amountof 1 wt % and 5 wt % based on the total weight of the mixture of granulefines and dopants. The following dopants were added: titanium dioxide(TiO₂), zinc oxide (ZnO), aluminum trihydroxide (ATH), and magnesiumhydroxide Mg(OH)₂.

The sintering was conducted at 1100° C., with a holding time of one hourat the maximum sintering temperature. The cooling regime was conductedunder controlled cooling including a temperature hold of two hours at850° C.

It can be seen in Table 3 that the best dopant effect with regard to anincrease in solar reflectance SR had ATH, especial ally if contained ata concentration of 5 wt %, which could nearly double the SR values from19% to 39%.

TABLE 3 Coupons made with granule fines (<150 μm) and different dopantsDopant Amount [wt % Solar Reflectance [%] No dopant — 19 ATH 1 23 5 39TiO2 1 19 5 34 ZnO 1 19 5 20 Mg(OH)2 1 16 5 21

Example 3

Investigation of ATH Doped Granule Fines

Coupons were prepared of granule fines as described in Examples 2 withvarying amounts of ATH (ATH Hydral 710 from Huber): 1 wt %, 5 wt %, 7.5wt % and 10 wt % based on the total weight of granule fines and ATH. Theexperiment focused on varying the maximum sintering temperature from1000° C. to 1150° C., and measuring the corresponding SR and L* values.

An interesting observation could be made at 1100° C. with 5 wt % ATH. Incomparison to coupons not containing ATH or low amounts of 1 wt %, thedrop in SR was much lower with 5 wt % ATH, see also Table 4. A highersintering temperature has the advantage of a higher strength of thesintered materials. Accordingly, it appears that a combination ofparameters, such as sintering temperature, amount and type of doping,and particle size of the granule fines may lead to a surprisingadvantage of properties, such as a high SR, a low L* and a highstrength.

TABLE 4 Coupons made of granule fines and different amounts of ATHsubjected to varying maximum sintering temperatures Amount of ATH [wt %]0 1 5 10 SR SR SR SR 1000° C. 47 48 50 54 1050° C. 42 43 48 53 1100° C.20 22 39 45

ATH doping was further investigated by comparing different coolingregimes with regard to the effect on solar reflectance and lightness L*.Coupons were prepared with granules fines containing 2.5 wt % ATH and7.5 t % ATH, subjected to high temperature sintering up to a maximumsintering temperature of 1100° C., and cooled according to two differentcooling regimes: a) free cooling and b) cooling including a temperaturehold at 850° C. for two hours.

It could be observed that next to a large increase in solar reflectanceby adding ATH, the cooling regime also had an influence of the finalsolar reflectance, but not on the lightness L* of the coupons: Insamples that were cooled by including a two hour temperature hold at850° C., the solar reflectance was about 4% to 5% higher in comparisonto samples that were allowed to free cool. In contrast, the L* valuesremained the same, independent of the conducted cooling regime. Theseeffects could be observed with 2.5 wt % ATH and 7.5 wt % ATH, see Table5.

TABLE 5 Comparison of different cooling regimes on SR and L* of ATHdoped granule fines, sintered up to 1100° C. maximum sinteringtemperature 2.5 wt % ATH 7.5 wt % ATH SR[%] L* SR[%] L* Free Cooling28.7 48 39.1 58 850° C./2 hours 33.4 48 43.4 58

Example 4

Effect of ATH Particle Size on Solar Reflectance

Coupons were prepared as described in Example 3, with varying amounts ofATH. Moreover, three different commercial ATH products from Huber withdifferent particle sizes were compared, as summarized in Table 6.

TABLE 6 Tested ATH products and related median particle sizes ATH Brand/Median Particle manufacturer Size [μm] C33 46.4 402 3.5 Hydral 710 1.2

As can be seen in FIG. 2, while ATH product C33 with the largestparticle size of 46.4 μm had nearly no influence on an increase of thesolar reflectance of the granule fines at any ATH concentration, theproducts with a much lower particle size (1.2 μm and 3.5 μm), especiallyat amounts of 5 wt % ATH and 10 wt % ATH, resulted in a clear increasein SR, and both products behaved very similar. The trend within thesesamples was that the smaller particle size product had the largestincrease in solar reflectance.

Example 5

Preparing of composite roofing granules.

In an Eirich Mixer R-04, 84 wt % granule fines of rhyolite with aparticle size smaller than 150 μm (the same as in Examples to 4), 1 wt %modified starch (ethylated starch from GPC), and 15 wt % water weremixed together to form green body granules. The mixing was conductedthat first the granule fines and the starch was dry mixed for oneminute, and thereafter the water was slowly added to the dry mixture andmixed at low intensity for another minute, followed by 5 minutes highintensity mixing to form the granules. Each batch produced about 1.75 kggreen composite granules.

After the granulation, the green composite particles were sized bysieving through a sieve having a 3.35 mm mesh size (size 6) and fallingon a sieve having a 0.425 mm mesh size (size 4), in order to removelarge and very fine particles. Thereafter, the green body granules weresubjected to high temperature sintering.

The green composite granules were sintered by heating at a rate of 5°C./min to a maximum sintering temperature of 1075° C. (1075 CP) and1100° C. (1100 CP), and cooled under controlled cooling, including atemperature hold at 850° C. for 2 hours.

Example 8

Pigment Coating

Composite granules of the type 1075 CP from Example 7 were pigmentcoated. The applied pigment coating was SR46 and applied by pan coating,wherein the granules and paint solution were shaken together to coat.

The pigment coating was able to maintain the solar reflectance but couldlower the L* value by 2-3 points. Furthermore, the pigment coating madethe composite granules more abrasion resistant and more durable ifsubjected to a multi-cycle freeze/thaw test. (see summary table 7 ofExample 9).

Example 9

Properties of Composite Roofing Granules

The composite roofing granules of Example 7 and 8 (1075 CP and 1100 CP)were tested for the following properties: SR, L*, crush strength,abrasion resistance, freeze/thaw durability, and roundness. Theexperiments include comparisons with base rock roofing granules (BaseRock), which were rock granules from the same type of rock (Rhyolite)from which the granule fines were obtained. Other comparison materialswere commercial pigment coated rock granules of CertainTeed (SR46); anda commercial product of composite granules called Firestone UltraWhitegranule from FireStone Building Products, which is mined kaolin crushedto granule size and calcined.

The testing results are summarized in Table 7 below.

TABLE 7 Summary of tested properties of prepared composite granules andcomparison with commercial products Pigment coated Firestone Base 1075CP 1100 CP 1075 CP CP Rock SR 46 SR [%] 28.0 19.0 28.0 66.6 16.6 31.8 L*42.2 35.5 40.5 82.3 47.8 44.7 Average Force to 48.9 55.3 66.0 38.4 96.9110 crush single particle [N] Abrasion 10.0 7.5 4.6 5.8 3.75 8.2Resistance - amount of 16/30 [% breakdown] Freeze/Thaw 10 99.60 99.7899.98 99.50 99.70 99.75 cycles [% retained] Freeze/Thaw 30 99.00 99.5099.95 99.43 99.65 99.70 cycles [% retained] Bulk density 0.921 1.0420.951 0.977 1.344 1.369 [g/cm³]

Measurement of Solar Reflectance SR and Lightness L*

The SR measurements have been made on coupons according to ASTM C-1549(2009). The lightness L* was measured with a HunterLab Labscan XEcolorimeter.

Measurement of the Crush Strength

Crush strength testing was conducted to simulate the loading of granuleson a roof. The granules of one batch were pre-sized by sieving through a6/10 screen combination, which corresponds to about 2.5 mm diametergranule size. The crush test was conducted by measuring the force tocrush one single particle, repeating the test on 30 single granules ofthe sized batch and calculating an average value of the test results.The crush test results of all tested materials are shown in Table 7 andin FIG. 3.

The results show that Base Rock and SR 46, CertainTeed's commercial rockproduct, have the highest strength, as expected. However the 1075 and1100 Composite Particles had a higher strength as Firestone's non-rockcommercial granule. The 1075 Pigment Coated Composite Particle showed afurther strength increase in comparison to non-coated 1075 CP and 1100CP.

Measurement of the Freeze/Thaw Durability

Freeze/Thaw testing was conducted to simulate the environment on theroof and to measure the effect on the composite granules. The granuleswere subjected to 6/40 sieving materials (passing through a 3.35 mm sizescreen (mesh size 6) and falling on a sieve having a 0.425 mm openings(mesh size 40), and then subjected to Freeze/Thaw cycling. Each cycleconsisted of submerging the granules in water, freezing them for 3hours, and then defrosting at room temperature for 1 hour. The testingwas completed for 10 and 30 cycles and the percentage of initialmaterial retained on the 40 mesh size screen was calculated. The resultsare shown in Table 7 and in FIG. 4. All materials retained 98% orgreater after 30 cycles. The pigment coated 1075 composite granules hadthe best performance (Pigment coated 1075 CP), outperforming Firestone'snon-rock granule after 30 cycles as well as the base rock granules.

Measurement of the Abrasion Resistance (ARMA 1993 Method)

Abrasion resistance testing was done to simulate the granule processingand handling conditions that the materials would experience throughoutthe typical shingle making process. The procedure is the test method ofthe Asphalt Roofing Manufacturer's Association (ARMA), titled AbrasionResistance of Roofing Granules, ARMA Granule Test Procedures Manual.

The test material was pre-sieved 12/16 and 100 g of the sieved granuleswere filled in a metal test tube, and the test tube was 100 timesrotated, see FIG. 5.

After 100 rotations the material was recovered, and the amount passing a30 mesh sieve determined and the percent breakdown calculated. The testsfor each sample were three times repeated and the average valuecalculated. The results for all tested granule materials are shown inFIG. 6.

Overall, the results show that all tested materials generated less than2 percent of 30/pan material. The pigment coated 1075 composite granuleshad equivalent performance to CertainTeed's current SR 46 granule andFirestone's non-rock granule for particle breakdown.

Measurement of the Bulk Density

The bulk density of all samples was measured by loosely filling a 10 mlcylinder having a volume of 13.68 cc with granules without applyingpressure, and measuring the weight of the cylinder content. The bulkdensities of the granule samples of the present disclosure, i.e., 1075CP, 1100 CP, and 1075 CP pigment coated, are shown in FIG. 7 and Table7. The bulk densities were compared with the bulk densities ofcommercial rock granules SR-46, Firestone composite granules, andrhyolite Base Rock granules. Granules representative of the presentdisclosure have much lower bulk densities then the rock-based granulesSR-46 and Base Rock, as well as Firestone granules.

In the foregoing specification, the concepts have been described withreference to specific embodiments. However, one of ordinary skill in theart appreciates that various modifications and changes can be madewithout departing from the scope of the invention as set forth in theclaims below. Accordingly, the specification and figures are to beregarded in an illustrative rather than a restrictive sense, and allsuch modifications are intended to be included within the scope of theinvention.

What is claimed is:
 1. A method of making a plurality of composite granules, comprising: forming green body granules comprising an aluminosilicate; heating the green body granules to form sintered granules; cooling the sintered granules according to a cooling regime, wherein the cooling regime comprises a temperature hold between 700° C. and 900° C. for at least one hour.
 2. The method of any of claim 1, wherein a difference in solar reflectance ΔSR of composite granules subjected to the temperature hold (SR_(TH)) in comparison to composite granules not subjected the temperature hold (SR_(F)) is at least 3%, with ΔSR=SR_(TH)−SR_(F).
 3. The method of claim 1, wherein the temperature hold is at least two hours.
 4. The method of claim 1, wherein the solar reflectance of the composite granules is at least 25%.
 5. The method of claim 1, wherein the L* value of the composite granules is not greater than
 50. 6. The method of claim 1, wherein forming of the green body granules includes adding of a solvent and a binder.
 7. The method of claim 6, wherein the binder is modified starch and the solvent is water.
 8. The method of claim 1, wherein forming of the green body granules includes adding of ATH in an amount of at least 2 wt % based on the total dry weight of the green body granules.
 9. The method of claim 8, wherein the ATH has a median particles size not greater than 30 μm.
 10. The method of claim 1, further including sizing the green body granules to a size of at least 0.3 mm and not greater than 3.0 mm.
 11. The method of claim 1, wherein heating is conducted up to a maximum sintering temperature of at least 1000° C.
 12. The method of claim 1, wherein heating is conducted up to a maximum sintering temperature of not greater than 1300° C.
 13. The method of claim 1, wherein the aluminosilicate is a natural rock including rhyolite, andesite, basalt, meta-basalt, or any combination thereof.
 14. The method of claim 1, wherein an amount of the aluminosilicate in the green body granules is at least 50 wt % based on the total weight of the green body granules.
 15. The method of claim 1, wherein the aluminosilicate of the green body granules has an average particle size not greater than 150 μm.
 16. The method of claim 1, wherein a bulk density of the composite granules is not greater than 1.0 g/m³.
 17. The method of claim 1, wherein the composite granules have an average crush strength of at least 45 N.
 18. The method of claim 1, wherein the green body granules are essentially free of TiO₂, ZnO₂, and Mg(OH)₂.
 19. A method of making a plurality of composite granules, comprising: forming a plurality of green body granules comprising an aluminosilicate; heating the green body granules to form sintered granules; and cooling the sintered composite granules at a cooling rate of not greater than 2° C. per minute to a temperature of 750° C.
 20. A plurality of composite granules, comprising: a bulk density not greater then 1.0 g/cm³; an amount of aluminosilicate of at least 50 wt % based on a total weight of the composite granules; an amount of aluminum trihydrate of at least 2 wt % based on the total weight of the composite granules; a solar reflectance of at least 25%; an L* value of not greater than 50; and an average crush strength of at least 45 N. 